<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      const user = {
        name: "jack",
        age: 20,
        allow: true,
        [Symbol("id")]: 100,
        admin: undefined,
        say() {},
      };
      const arr = [1, 2, 3, 4, 5, Symbol("id"), undefined, function say() {}];

      console.log(JSON.stringify(user));
      console.log(JSON.stringify(arr));
    </script>
  </body>
</html>
